In recent years, lithium ion batteries which are light-weighted and high capacity are mainly used as a power source of electronic equipment represented by cellular phones, personal computers and the like.
However, increase in power consumption relating to development of the electronic equipment with higher performance is causing problems of (1) inability to secure sufficient electric power, (2) shortened continuous operating time even with necessary electric power secured, and (3) a long charging time being required.
Under these circumstances, fuel cells are attracting attention as a power source which replaces the lithium ion batteries. Particularly, Direct Methanol Fuel Cells (DMFCs) which use methanol as fuel are regarded as promising. The DMFCs have a Membrane Electrode Assembly (MEA) constituted of a fuel electrode, an air electrode, and an electrolyte membrane for supplying methanol water solution to the fuel electrode while supplying air to the air electrode. The methanol supplied to the fuel electrode is decomposed by a catalyst and hydrogen ions are created. The hydrogen ions pass through the electrolyte membrane and react with oxygen existing in the air at the air electrode. The DMFCs generate electric power through a series of these reactions.
Since the DMFCs can provide high-density energy as compared with the lithium ion batteries, they can cope with the increased power consumption of the electronic equipment. Moreover, preparing reserve fuels for the DMFCs allows continuous use of the electronic equipment without the necessity of a long charging time as in the lithium ion batteries. Further, since the DMFCs do not need devices such as a reformer which produces hydrogen, reduction in size and weight of the DMFCs is possible, which is regarded as one of the advantages of the DMFCs over other fuel cells.
One of the members constituting the DMFC is a current collecting plate. In order to achieve smaller and lighter fuel cells, a flexible circuit board is used as a current collecting plate (see, e.g., Patent Literature 1). In the flexible circuit board, a conductor layer constituting a current collector is formed on one side of a flexible base material which is made of polyimide and the like. The current collector has openings provided for supplying methanol or air to the MEA.
In order to maintain characteristics such as an output voltage of the fuel cell, the current collector is required to have corrosion resistance against methanol and intermediate products, such as formic acid, which are created in the process of decomposing the methanol. Accordingly, Patent Literature 2 discloses a flexible circuit board in which a conductor layer as a current collector is coated with a carbon containing layer. The carbon containing layer is made of a resin composition containing carbons such as carbon black in a resin material such as polyimide.